The present invention relates to the generation of coherent x-rays. More specifically, the present invention relates to direct photon pumping in a Na-Ne system where a thermal buffer is inserted therebetween.
For many years now, there have been a variety of proposed schemes suggesting ways to create a population inversion and subsequent gain in the x-ray region. (A population inversion exists when the upper energy level in a transition is overpopulated relative to the lower energy level and is a necessary requirement for lasing to occur.) U.S. Pat. No. 4,206,364 to Dixon et al. describes a one sided laser irradiation scheme using tungsten blocks to create a channel for plasma from a carbon target. Population inversion occurs in the expanding carbon plasma. U.S. Pat. No. 4,229,708 to Mani et al. concerns producing lithium-like atoms or ions using one-sided soft x-ray photon fluxes.
Another scheme involves the flashlamp concept where the radiated flux from one plasma pumping another plasma creates conditions which result in coherent radiation in the soft x-ray regions. See A. V. Vinogradov, I. I. Sobel'man, and E. A. Yokov, Sov. J. Quantum. Electron 5, 59 (1975); B. A. Norton and N. J. Peacock, J. Phys. B 6, 989 (1975); J. P. Apruzese, J. Davis, and K. G. Whitney, J. Phys, B 11, L643 (1978); R. H. Dixon and R. C. Elton, J. Opt. Soc. Am. B 1, 232 (1984), and references therein. There are several cases where the coincidence between the pumping and absorbing lines is close enough to merit strong consideration as a possible lasing combination. For example, K-shell lines from Mg, Al, or Si are reasonably well matched to several fluorinelike Kr lines. Two such schemes utilize a Si XIII-Al III system and a Na X-Ne IX system. The Na-Ne scheme is particularly interesting because the lines match to two parts in 10.sup.4 at a wavelength of 11 angstroms. An energy level diagram of this scheme is shown in FIG. 2.
In the Na-Ne approach, photons emitted from one element (Na) impinge upon and pump the upper lasing level of the second element (Ne). This is one of the most promising approaches but it has not succeeded because the conditions required in the pumped and pumping plasmas are drastically different and therefore difficult to acheve when they are in close physical proximity.
More specifically, the higher temperature that is present in order for the Na to function as a pump will propagate in a thermal wave over a finite time into the Ne creating an overall isothermal state which precludes the Ne from being at the lower temperature and density necessary to produce the desired x-ray lasing. This is particularly disastrous if the Ne is in contact with the Na. However, if the two materials are separated by any appreciable distance, then the efficiency of the system is lost due to solid angle effects.